• Journal of Korea Multimedia Society
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• v.23 no.9
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• pp.1164-1170
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• 2020

In this paper, we consider the wireless-powered backscatter communication which consists of a power beacon, a source, a relay, and a destination. For the proposed wireless-powered backscatter communication, the source transmits its signals to both the relay and the destination via a backscattering channel and the relay which has a rechargeable battery performs an energy harvesting as well as an information forwarding based on the time switching relay (TSR) protocol. Based on the decode-and-forward (DF) relay transmission, we investigate performances of the proposed system in terms of outage probability and transmission rate in which the exact performance analysis of outage probability is given. Finally, some numerical examples are given to verify our provided analytical results for different system conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.2
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• pp.565-581
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• 2019

This paper investigates the wireless powered two way relay network (WPTWRN), where two single-antenna users and one single-antenna relay firstly harvest energy from signals emitted by a multi-antenna power beacon (PB) and then two users exchange information with the help of the relay by using their harvested energies. In order to improve the energy transfer efficiency, energy beamforming at the PB is deployed. For such a network, to explore the performance limit of the presented WPTWRN, an optimization problem is formulated to obtain the achievable rate region bounds by jointly optimizing the time allocation and energy beamforming design. As the optimization problem is non-convex, it is first transformed to be a convex problem by using variable substitutions and semidefinite relaxation (SDR) and then solve it efficiently. It is proved that the proposed method achieves the global optimum. Simulation results show that the achievable rate region of the presented WPTWRN architecture outperforms that of wireless powered one way relay network architecture. Results also show that the relay location has significant impact on achievable rate region of the WPTWRN.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.8
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• pp.3542-3566
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• 2018

In this paper, we investigate a buffer-aided wireless powered cooperative communication network (WPCCN), in which the source and relay harvest the energy from a dedicated power beacon via wireless energy transfer, then the source transmits the data to the destination through the relay. Both the source and relay are equipped with an energy buffer to store the harvested energy in the energy transfer stage. In addition, the relay is equipped with a data buffer and can temporarily store the received information. Considering the buffer-aided WPCCN, we propose two buffer-aided relaying protocols, which named as the buffer-aided harvest-then-transmit (HtT) protocol and the buffer-aided joint mode selection and power allocation (JMSPA) protocol, respectively. For the buffer-aided HtT protocol, the time-averaged achievable rate is obtained in closed form. For the buffer-aided JMSPA protocol, the optimal adaptive mode selection scheme and power allocation scheme, which jointly maximize the time-averaged throughput of system, are obtained by employing the Lyapunov optimization theory. Furthermore, we drive the theoretical bounds on the time-averaged achievable rate and time-averaged delay, then present the throughput-delay tradeoff achieved by the joint JMSPA protocol. Simulation results validate the throughput performance gain of the proposed buffer-aided relaying protocols and verify the theoretical analysis.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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• pp.1889-1910
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• 2017

This paper investigates a protocol so-called Adaptive Harvest Then Transmit (AHTT) for wireless powered communication networks (WPCNs) in multiple-input single-output (MISO) downlink systems, which assists in transmitting signals from a multi-antenna transmitter to a single-antenna receiver. Particularly, the power constrained relay is supplied with power by utilizing radio frequency (RF) signals from the source. In order to take advantage of multiple antennas, two different linear processing schemes, including Maximum Ratio Combining (MRC) and Selection Combination (SC) are studied. The system outage capacity and ergodic capacity are evaluated for performance analysis. Furthermore, the optimal power allocation is also considered. Our numerical and simulation results prove that the implementation of multiple antennas helps boost the energy harvesting capability. Therefore, this paper puts forward a new way to the energy efficiency (EE) enhancement, which contributes to better system performance.

• Journal of the Korea Society of Computer and Information
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• v.22 no.5
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• pp.81-88
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• 2017

Solar-powered wireless sensor nodes can use extra energy to obtain additional data to increase the precision. However, if the amount of data sensed is increased indiscriminately, the overhead of relay nodes may increase, and their energy may be exhausted. In this paper, we introduce a sensing and compression rate selection scheme to increase the amount of data obtained while preventing energy exhaustion. In this scheme, the neighbor nodes of the sink node determine the limit of data to be transmitted according to the allocated energy and their descendant nodes, and the other nodes select a compression algorithm appropriate to the allocated energy and the limitation of data to be transmitted. A simulation result verifies that the proposed scheme gathers more data with a lower number of blackout nodes than other schemes. We also found that it adapts better to changes in node density and the amount of energy harvested.

• Journal of the Korea Society of Computer and Information
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• v.22 no.7
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• pp.101-108
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• 2017

A wireless image sensor node collecting image data for environmental monitoring or surveillance requires a large amount of energy to transmit the huge amount of video data. Even though solar energy can be used to overcome the energy constraint, since the collected energy is also limited, an efficient energy management scheme for transmitting a large amount of video data is needed. In this paper, we propose a method to reduce the number of blackout nodes and increase the amount of gathered data by selecting an appropriate video coding method according to the energy condition of the node in a solar-powered wireless video sensor network. This scheme allocates the amount of energy that can be used over time in order to seamlessly collect data regardless of night or day, and selects a high compression coding method when the allocated energy is large and a low compression coding when the quota is low. Thereby, it reduces the blackout of the relay node and increases the amount of data obtained at the sink node by allowing the data to be transmitted continuously. Also, if the energy is lower than operating normaly, the frame rate is adjusted to prevent the energy exhaustion of nodes. Simulation results show that the proposed scheme suppresses the energy exhaustion of the relay node and collects more data than other schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.10
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• pp.1849-1854
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• 2017

Recently, RF energy harvesting, in which energy is collected from the external RF signals, is considered as a promising technology to resolve the energy shortage problem of wireless sensors. In addition, it is important to guarantee secure communication between sensors for implementing Internet-of-Things. In this paper, we propose a power splitting-based network analog coding for maximizing a physical layer security in 2-hop networks where the wireless-powered relay can harvest energy from the signals transmitted by two sources. We formulate systems where two sources, relay, and eavesdropper exist, and find an optimal power splitting ratio for maximizing the minimum required secrecy capacity using an exhaustive search. Through simulations under various environments, it is demonstrated that the proposed scheme improves the minimum required secrecy capacity by preventing the eavesdropper from overhearing source signals, compared to the conventional scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.5
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• pp.2009-2028
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• 2018

Considering a dual-hop energy-harvesting (EH) relaying system, this paper advocates novel relaying protocols based on adaptive time power switching-based relaying (AR) architecture for amplify-and-forward (AF) mode. We introduce novel system model relaying network with impacts of co-channel interference (CCI) and derive analytical expressions for the average harvested energy, outage probability, and the optimal throughput of the information transmission link, taking into account the effect of CCI from neighbor cellular users. In particular, we consider such neighbor users procedure CCI both on the relay and destination nodes. Theoretical results show that, in comparison with the conventional solutions, the proposed model can achieve optimal throughput efficiency for sufficiently small threshold SNR with condition of reasonable controlling time switching fractions and power splitting fractions in concerned AR protocol. We also explore impacts of transmission distances in each hop, transmission rate, the other key parameters of AR to throughput performance for different channel models. Simulation results are presented to corroborate the proposed methodology.